Endolymphatic hydrops is an enlargement of the scala media which occurs in various pathological conditions, e.g. Meniere's disease. Study of hydrops is highly clinically relevant in that it is one of the most common causes of hearing impairment in humans. The purpose of the present research is to follow the normal progression of endolymphatic hydrops as it occurs in the guniea pig and/or gerbil. To date, this has not been possible because of the lack of a noninvasive technique for assessing the dimensions of the scala media. The guinea pig is currently an accepted model of endolymphatic hydrops and it can be artificially created by occluding the endolymphatic duct; preliminary data obtained with the mustached bat cochlea ex vivo has shown the feasibility of such a study. After the normal sequence of development of hydrops is described, then various manipulations, i.e., different drugs without serious side effects to the animals, can be used to try to alleviate this condition. Since the final goal of this research is to observe the in vivo the progression of endolymphatic hydrops, the smaller gerbil may be the animal of choice.